Potential Predators Research Articles

New Pyridyl and Dihydroisoquinoline Alkaloids Isolated from the Chevron Nemertean Amphiporus angulatus.

Nemertean worms contain toxins that are used to paralyze their prey and to deter potential predators. Hoplonemerteans often contain pyridyl alkaloids like anabaseine that act through nicotinic acetylcholine receptors and crustacean chemoreceptors. The chemical reactivity of anabaseine, the first nemertean alkaloid to be identified, has been exploited to make drug candidates selective for alpha7 subtype nAChRs. GTS-21, a drug candidate based on the anabaseine scaffold, has pro-cognitive and anti-inflammatory actions in animal models. The circumpolar chevron hoplonemertean Amphiporus angulatus contains a multitude of pyridyl compounds with neurotoxic, anti-feeding, and anti-fouling activities. Here, we report the isolation and structural identification of five new compounds, doubling the number of pyridyl alkaloids known to occur in this species. One compound is an isomer of the tobacco alkaloid anatabine, another is a unique dihydroisoquinoline, and three are analogs of the tetrapyridyl nemertelline. The structural characteristics of these ten compounds suggest several possible pathways for their biosynthesis.

Does novelty influence the foraging decisions of a scavenger?

Acquiring knowledge about the environment is crucial for survival. Animals, often driven by their exploratory tendencies, gather valuable information regarding food resources, shelter, mating partners, etc. However, neophobia, or avoiding novel environmental stimuli, can constrain their exploratory behaviour. While neophobia can reduce potential predation risks, decreased exploratory behaviour resulting from it may limit the ability to discover highly rewarding resources. Dogs (Canis familiaris) living in semi-urban and urban environments as free-ranging populations, although subject to various selection forces, typically have negligible predation pressure. These dogs are scavengers in human-dominated environments; thus, selection against object-neophobia can provide benefits when searching for novel food resources. Although captive pack-living dogs are known to be less neophobic than their closest living ancestors, wolves (Canis lupus), little is known about free-ranging dogs' behavioural responses to novel objects, particularly in foraging contexts. Using an object choice experiment, we tested 259 free-ranging dogs from two age classes, adult and juvenile, to investigate their object-neophobia in a scavenging context. We employed a between-subject study design, providing dogs with a familiar and a potentially novel object, both baited with equal, hidden food items. Adult and juvenile dogs significantly inspected the novel object first compared to the familiar one, even when the hidden food item was partially visible. To validate these findings, we compared novel objects with different strengths of olfactory cues (baited vs. false-baited) and found that they were inspected comparably by adults and juveniles. No significant differences were found in the latencies to inspect the objects, suggesting that free-ranging dogs may still be cautious when exploring their environments. These results indicate that free-ranging dogs, evidently from an early ontogenetic phase, do not show object-neophobia, as demonstrated by their preference for novel over familiar food sources. We conclude that little to no constraint of neophobia on exploratory behaviour in semi-urban and urban-dwelling animals can guide foraging decision-making processes, providing adaptive benefits.

Urban noise slows down the antipredator reaction of Eurasian Magpies

Urban areas are known to have high levels of noise pollution, which can impact an animal’s antipredator behavior. Noise can either distract the animal or mask the sounds of a predator, increasing the animal’s vulnerability to predation. However, the prey may increase vigilance in noisier environments, thus reducing energy and time spent on other activities. Alert Distance (AD) refers to the distance at which an animal becomes alert to a potential predator approaching. Flight Initiation Distance (FID) is the distance from the potential predator at which the animal flees. We studied the impact of ambient noise pollution on the AD and a corrected FID (FID/AD) of Eurasian Magpies (Pica pica) using a field investigator as a potential predator walking towards birds at a constant speed. We found that the noise level did not affect the AD. Still, noise had a negative effect on the Eurasian Magpies’ FID/ADs, suggesting that noise may slow their reaction to a potential threat but not their ability to detect it. Thus, our research highlights that urban noise pollution can increase an individual's vulnerability to predation, even when predators are still detectable. Ambient noise may distract the bird by diverting some of its limited attention and causing a delayed response to the predators. Alternatively, noise could be masking auditory cues that would have otherwise been added together with visual cues to cause an enhanced response. More research is necessary to understand the effects of noise pollution on the antipredator behavior of birds in urban areas, taking into account the specific strategies and adaptations of each species.

Updated distribution of Zoropsis spinimana (Dufour, 1820; Araneae: Zoropsidae) in Germany and novel insights into its ecology based on a citizen science survey

In Germany, Zoropsis spinimana (Dufour, 1820) is an introduced, likely synanthropic spider species. Here, we report the results of a nationwide mapping appeal conducted by the citizen science platform NABU-naturgucker.de, used to assemble live distributional data for the species in Germany. With the help of media interest in this species, we gathered a valuable dataset and a large image gallery of the species. In just five weeks, we received more than 15,000 records, representing a 2.3-fold increase in occupied territory compared to previous knowledge. By analyzing the data in detail, we obtained novel insights into the ecology and eco-geography of Z. spinimana in Germany, including information on prey, coloration, potential predators, altitudinal distribution and temporal appearance, along with two cases of accidental human translocation.

Social display in the Curaçao Whiptail (Cnemidophorus murinus Laurenti)

Three teiid species (Squamata: Teiidae) are endemic to the ABC islands (Aruba, Bonaire, and Curaçao) of the former Netherlands Antilles: the Aruba Whiptail (Cnemidophorus arubensis) of Aruba, the Bonaire Whiptail (C. ruthveni) of Bonaire and Klein-Bonaire, and the Curaçao Whiptail (C. murinus) of Curaçao and Klein-Curaçao. Before now, social displays have been described only for one of these three species: C. ruthveni (Baird et al. 2003). All three species engage in an arm-waving display that involves forelimb circumduction (Baird et al. 2003; van Buurt 2005; van Buurt 2011), which conveys social signals to conspecifics in some iguanian and lacertid lizard species (Carpenter et al. 1970; Verbeek 1972; Mitchell 1973). However, this behavior in the ABC island species of Cnemidophorus has not been shown to have a social function (Baird et al. 2003). Instead, experimental evidence demonstrates that in C. ruthveni it functions as a pursuit deterrent display that is performed in response to approaching humans, whom the lizard may view as potential predators (Cooper et al. 2004), although there are not yet any published reports of C. ruthveni performing the display in response to the approach of a non-human predator. My observations and those of others (van Buurt 2011) also confirm that in C. arubensis the display is performed in response to approaching humans.

Prey stage preference of Amblyseius paraaerialis (Acari: Phytoseiidae) on varied life stages of the spider mites Tetranychus urticae, Tetranychus macfarlanei and Oligonychus biharensis (Acari: Tetranychidae) and exploring the mass rearing possibilities of this predatory mite on alternative diets.

Spider mites Tetranychus urticae, Tetranychus macfarlanei and Oligonychus biharensis are considered to be highly polyphagous in nature and causes severe damage to a wide range of plants around the world. Amblyseius paraaerialis is an efficient phytoseiid predator of spider mites with a potential to survive on both natural and alternative diets. Evaluation of predatory potential and prey stage preference provides valuable information on the efficacy of the predatory species in controlling mite population. Feeding experiments were conducted on mulberry leaf discs under the laboratory conditions of 30 ± 2 °C and 70 ± 5% relative humidity (RH). After 24h of feeding experiment, the adult female predator exhibited a significant preference in feeding towards the eggs of T. macfarlanei (42.6%) and the larval stages of T. urticae (46%) and O. biharensis (25.3%). The mass rearing possibilities of A. paraaerialis was tested by tracking and comparing the developmental duration of individual life stages on varied food sources like, honey, castor (Ricinus communis) pollen, honey-pollen mixture and mixed life stages of T. urticae. The predator was failed to complete its development on honey and pollen when supplied separately. However it was successfully developed on honey-pollen mixture and mixed life stages of T. urticae. The developmental studies unravelled a shortest developmental duration and an extended adult longevity and lifespan of A. paraaerialis when reared on the alternative diet, thus opened up the mass rearing possibility of the predatory species under laboratory conditions.

Employing an innovative underwater camera to improve electronic monitoring in the commercial Gulf of Mexico reef fish fishery.

Vessel electronic monitoring (EM) systems used in fisheries around the world apply a variety of cameras to record catch as it is brought on deck and during fish processing activities. In EM work conducted by the Center for Fisheries Electronic Monitoring at Mote (CFEMM) in the Gulf of Mexico commercial reef fish fishery, there was a need to improve upon current technologies to enhance camera views for accurate species identification of large sharks, particularly those that were released while underwater at the vessel side or underneath the hull. This paper describes how this problem was addressed with the development of the first known EM system integrated underwater camera (UCAM) with a specialized vessel-specific deployment device on a bottom longline reef fish vessel. Data are presented based on blind video reviews from CFEMM trained reviewers of the resulting UCAM video footage compared with video from only the overhead EM cameras from 68 gear retrievals collected from eight fishing trips. Results revealed that the UCAM was a successful tool for capturing clear underwater video footage of released large (>2m) sharks to enable reviewers to improve individual species identification, determination, and fate by 34.4%. This was particularly important for obtaining data on incidental catches of large protected shark species. It also provided clear underwater imagery of the presence of potential predators such as marine mammals close to the vessel, more specifically bottlenose dolphin (Tursiops truncatus) during gear retrieval, which often damaged or removed catch. This information is intended to assist researchers in need of gathering critical data on bycatch in close proximity to a vessel in which conventional overhead EM cameras are limited.

The effects of cyflumetofen on life history traits and population parameters of Amblyseius swirskii</p >

Even as new chemical substances show promise as selectivity for controlling pests due to their high effectiveness in inhibiting pests, their side effects on non-target organisms must nevertheless be evaluated before they can be included in integrated pest management systems. We examined both lethal and sublethal (LC10 and LC30) effects of cyflumetofen on the predatory potential of the Amblyseius swirskii Athias Henriot (Acari: Phytoseiidae) which is among the most dominant mite predators in tropical agricultural agroecosystems. The experiments were performed under laboratory conditions at 25 ± 2°C, 65 ± 5% relative humidity (RH), and a photoperiod of 16:8 (L: D) hours. Results were analyzed based on age-stage, two-sex life table analysis. The data showed that sublethal concentrations of the pesticides suppress fecundity, total life span (both female and male individuals), and the intrinsic and finite rate of increase significantly. The result show, the fecundity in the LC10, LC30, and control was 14.97, 11.87, and 17.28, eggs/female for LC10 and LC30, respectively, showing significant differences. The values of the intrinsic rate of increase (r) on the above-mentioned concentrations were 0.1333, 0.1166, and 0.1430 day-1, respectively. Consequently, according to the data, it seems that the selected acaricide is not suitable to use with A. swiriskii in integrated pest management programs due to their unfavorable effects on the population parameters of this predatory mite.

Chemical Cues Released by Predators’ Consumption of Heterospecific Prey Alter the Embryogenesis of Zebrafish

Environmentally cued hatching is prevalent, diverse, and crucial to many animals’ survival. Fish embryos use a variety of chemical cues to initiate hatching to avoid potential predators, yet the function of chemical cues released from the predatory consumption of heterospecific prey is largely unknown. Zebra cichlids (Metriaclima estherae) are ferocious predators that can feed on medaka (Oryzias latipes), though it is impossible for this to occur in their natural habitat. Zebrafish (Danio rerio) embryos have been employed as experimental subjects due to their sensitivity to a variety of chemical signals. In this study, zebrafish embryos were subjected to three types of chemical signals: predator cues (PCs, released from cichlids), heterospecific cues (HCs, released from medaka), and heterospecific dietary cues (HDCs, released from cichlids that have ingested medaka). As a result, the hatching times of zebrafish embryos were accelerated by 6.8% and 12.6% by PCs and HDCs, respectively. PCs and HDCs cause significantly reduced morphology in zebrafish embryos, including regarding total length, eye length, dorsal fin length, trunk height, caudal fin height, and body cavity, and increase yolk sac height. The PCs and HDCs diminished the larvae’s motion at 120 and 144 h post fertilization (hpf), which could be attributed to non-developmental embryogenesis. Overall, the impacts of HDCs on embryonic hatching, developmental morphology, and locomotor were more pronounced in comparison with PCs. Our findings demonstrate that predators’ dietary cues, even those released after predation on heterospecific prey, can modify embryogenesis, highlighting the critical functions of chemical signals in predation risk assessment using embryos.

The effect of four different object properties on latency to approach in Goffin's cockatoos (Cacatua goffiniana).

Neophobia and neophilia can be lifesaving as they can facilitate foraging while avoiding predation or intoxication. We investigated the extent to which Goffin's cockatoos (Cacatua goffiniana) exhibit ecollogically relevant and quantifiable neophobic responses toward specific object properties. Twelve cockatoos were presented with 12 novel objects grouped into four distinct categories with unique features: size, color, reflective capacity, and shape. The cockatoos were tested by measuring their latency to approach a high-quality food reward for both novel and control scenarios. Age and sex did not affect the latency to approach food in the presence of a novel object in this species. Additionally, we found no significant differences between the objects of the reflective and color categories. This result is likely due to the plasticity of neophobic behavior related to the benefits and costs of approaching novel stimuli. The cockatoos were significantly slower to approach food in the presence of objects larger than their body size than objects of a similar or smaller size, a phenomenon possibly explained by the increased risk of approaching unknown objects large enough to be a potential predator. They were also significantly more hesitant to approach food in the presence of elongated objects, a phenomenon potentially explained by an ecologically relevant avoidance of snakes. The extent of this neophobia was statistically similar at a group level, indicating that avoidance of elongated and large objects could be an adaptive response aiding survival under natural circumstances and that snakes may impose strong selective pressures on this species. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Investigation the Potential of Myopopone castanea Smith (Hymenoptera: Formicidae) as Bio-Agent of Oryctes rhinoceros (Coleoptera: Scarabaediae) in Oil Palm Plantations

The Myopopone castanea Smith (Hymenoptera: Formicidae) is a predator of Oryctes rhinoceros Linn larvae, the main pest on oil palm plantations. These predatory ants have potential as biological agents because they have similar niches to their prey. This research aimed to explore the presence and potential of M. castanea as bio-agents in oil palm plantations and obtain knowledge about the abiotic environment of Myopopone castanea ant nests. The research was conducted in oil palm plantations owned by PTPN 4 Adolina, PTPN 2 Pagar Merbau, and smallholder oil palm plantations in Binjai, North Sumatra Province. Sampling was conducted using the purposive sampling method and as many as 10 sample points in each plantation. The results showed that the average temperature and humidity in the ant nests were 29.4 °C and 70.5%, respectively. The number of individual ants in a colony varied greatly in number and developmental stages. The predation potential of Myopopone castanea ants in the field reached 50.3% for five days of exposure in smallholder plantations and 46,9% in Adolina Plantation. This research could be the opportunity to use Myopopone castanea ants as a biological control for larvae Oryctes rhinoceros in oil palm plantations.

The effect of artificial light at night on a nocturnalprimate.

Anthropogenic disturbance is a major threat to biodiversity. An anthropogenic disturbance that is rarely addressed for nonhuman primates is the effect of artificial light at night (ALAN) which is defined by the spread of artificial lighting at night which eliminates natural darkness. Artificial light at night can result from streetlights, or indirectly from sky glow (artificial light that is scattered and reflected back to earth by the atmosphere). Research has demonstrated that artificial lighting causes changes in animal behavior, reproductive success, survivorship, as well as can alter the composition of the communities. The goal of this paper is to explore how the behavior of spectral tarsiers, Tarsius spectrumgurskyae, is modified in response to artificial light. We conducted this study at Tangkoko Nature Reserve on the easternmost tip of the northern arm of Sulawesi, Indonesia. The results of this study suggest that in response to artificial light tarsiers increase their time spent travelling and foraging, left their sleeping sites earlier and returned to them later thereby extending their daily activity time. The tarsiers also left their sleeping trees at lower heights, gave fewer vocalizations and fewer alarm calls each night in response to the additional artificial light. The tarsier's lengthened night might be leading to a change in interspecific competition for food as well as increase the ability of potential predators to locate the tarsiers. Additional research on the effect of ALAN on primates is clearly needed.

First report of the predatory potential and functional response of the red flower assassin bug Rhynocoris segmentarius (Germar), a natural enemy of Spodoptera frugiperda (J.E. Smith)

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is currently the most devastating invasive arthropod pest of maize in sub-Saharan Africa. Following its first report in Ghana in 2016, control has been reliant mainly on synthetic chemicals. However, biocontrol has been an effective, sustainable, cheaper, and environmentally friendly option for FAW management. We tested the potential of the red flower assassin bug, Rhynocoris segmentarius (Germar) (Hemiptera: Reduviidae) as a natural enemy candidate for augmentative biocontrol of FAW in Ghana by assessing its predatory rate and functional response under laboratory conditions in Ghana. The feeding responses of the five nymphal instars and adults (female and male) of R. segmentarius were tested against three larvae ages of FAW: (i) < 1 day old or newly emerged (NE), (ii) 2 days old, and (iii) 6 days old, at six different prey densities: 5, 15, 25, 30, 35, and 40, respectively. All life-stages of R. segmentarius successfully attacked, killed, and fed on the larvae of S. frugiperda, and exhibited a Type II functional response. However, the first and second nymphal stages of R. segmentarius did not successfully attack or kill six-day-old FAW larvae. Females had a significantly higher attack rate (7.79 ± 1.01) and the shortest handling time (1.17 x 10–1) than all life-stages. Our results suggest that R. segmentarius is a potential candidate for augmentative biocontrol of S. frugiperda.

Changes in vegetation complexity during the development of rice ecosystems affect orb‐weaving spider‐prey trophic networks

Abstract Temporal change in vegetation complexity and field management may interactively affect the structure of predator–prey networks in agroecosystems and consequently alter the biocontrol potential of predators. There is a limited number of studies that have addressed these questions for generalist predator–prey networks. We investigated how vegetation complexity during crop development and management type (conventional vs. organic) affect the trophic networks of orb‐weaving spiders and their prey in rainfed lowland rice ecosystems in southern Thailand. Specifically, we investigated orb‐weaving spiders and prey composition, prey selectivity and network structure. Overall, orb‐weaving spiders captured mostly detritus‐associated Diptera, aquatic‐associated Ephemeroptera and Hemiptera pests. The increasing vegetation complexity during rice development significantly restructured the network of orb‐weaving spiders and prey, while field management had only a marginal effect. The increased vegetation complexity during rice development led to an increased number of weak trophic interactions in comparison to few but strong interactions in simple vegetation. Our results indicate that increasing the number of spider species per prey taxon (prey vulnerability) in late rice season may enhance their top‐down control of prey including rice pests. This study also highlights that the network complexity and the stability of rice ecosystems increased during the rice growing season as the vegetation became more complex. Future practices could look for a way to support the densities of detritus and aquatic insects and to artificially increase habitat complexity during the early stage of rice development to improve the biocontrol services provided by the orb‐weaving spiders.

Potential effects of avian predators on the behaviour of the Little Bustard Tetrax tetrax during the display season in a cereal pseudo-steppe

The Little Bustard Tetrax tetrax is an endangered steppe bird whose last remaining breeding populations in Catalonia (NW Spain) are located in the Lleida plains. Although the decline in this population is mainly associated with habitat loss and degradation due to agricultural intensification and urban encroachment, the proliferation of predators, some favoured by hu- mans, may also be having negative effects on this population, either through direct predation or indirect effects on behaviour and survival. Here, we describe the type of behavioural response exhibited by Little Bustards during the display season when they encounter a potential avian predator and discuss the possible indirect effects of these interactions. During counts carried out in the springs of 2010–2022 in three Special Protection Areas in the Lleida plains, 88 encounters between Little Bustards and eight species of avian predators were recorded. Among them, the Western Marsh Harrier Circus aeruginosus, Montagu’s Harrier C. pygargus and the Yellow-legged Gull Larus michahellis were the most frequent species involved in these encounters, although only the Yellow-legged Gull conducted deliberate attacks in a consistent way. Irrespective of the predator or its attitude, most encounters resulted in the Little Bustard being flushed. The number of encounters were higher at the beginning of the mating season, which may prevent Little Bustards from settling in otherwise suitable areas of habitat. The flushing of the bustards may increase the risk of collision with power lines and reduce mating success. Since the number of encounters between Yellow-legged Gulls and Little Bustards seems to have increased in recent years in the study area, we believe that there is a need to conduct further studies to understand how these interactions affect the population dynamics and conservation of this endangered species.

Long read genome assembly of Automeris io (Lepidoptera: Saturniidae) an emerging model for the evolution of deimatic displays.

Automeris moths are a morphologically diverse group with 135 described species that have a geographic range that spans from the New World temperate zone to the Neotropics. Many Automeris have elaborate hindwing eyespots that are thought to deter or disrupt the attack of potential predators, allowing the moth time to escape. The Io moth (Automeris io), known for its striking eyespots, is a well-studied species within the genus and is an emerging model system to study the evolution of deimatism. Existing research on the eyespot pattern development will be augmented by genomic resources that allow experimental manipulation of this emerging model. Here, we present a high-quality, PacBio HiFi genome assembly for Io moth to aid existing research on the molecular development of eyespots and future research on other deimatic traits. This 490 Mb assembly is highly contiguous (N50 = 15.78 mbs) and complete (benchmarking universal single-copy orthologs = 98.4%). Additionally, we were able to recover orthologs of genes previously identified as being involved in wing pattern formation and movement.

Clay larvae do not accurately measure biogeographic patterns in predation

AbstractAimSpatial variation in predation can shape geographic patterns in ecology and evolution, but testing how predation varies across ecosystems is challenging as differing species compositions and defensive adaptations can mask underlying patterns. Recently, biogeography has borrowed a tool from ecology: clay prey models. But clay models have not been adequately tested for geographic comparisons, and a well‐known problem –that clay prey only appeal to a subset of potential predators– could bias detected geographic patterns whenever the relative importance of predator guilds varies among sites. Here, we test whether clay larvae accurately capture geographic differences in predation on real larvae.Location90° of latitude and &gt;2000 m elevation across the Americas.TaxonVertebrate and invertebrate predation on ‘superworms’ (Zophobas larvae).MethodsAcross six sites that vary dramatically in latitude, elevation, and biome, we quantified predation on live, dead, and clay larvae. We physically excluded vertebrate predators from some larvae to distinguish total predation and invertebrate‐only predation.ResultsPredation on live superworms almost doubled from our high‐elevation high‐latitude site to our low‐elevation tropical site. Geographic patterns were consistent among live and dead larvae, but clay larvae missed extremely high predation at some sites and therefore mis‐measured true geographic patterns. Clay larvae did a particularly bad job at capturing geographic patterns in predation by invertebrates, although sample sizes for invertebrate predation were small.Main ConclusionsClay larvae are inappropriate for comparing predation rates across sites. They should be abandoned for biogeographic studies and reserved for comparisons within, rather than across, predator communities.

Effect of fungicides on the functional response of Neoseiulus longispinosus (Phytoseiidae) to Tetranychus urticae (Tetranychidae) eggs

ABSTRACT The present study was performed to investigate the effect of fungicides (mancozeb, copper oxychloride, thiophanate methyl, and metalaxyl + mancozeb) on the functional response of a phytoseiid predator, Neoseiulus longispinosus (Evans), to eggs of Tetranychus urticae Koch. The predatory mite females were treated with fungicides and after 48 h, progeny from live females were evaluated for the residual toxicity effect on the functional response of predatory mites. All the tested stages of N. longispinosus (protonymph, deutonymph, adult female and male) exhibited a type II functional response to eggs of T. urticae in fungicide treatments and untreated control. With an increase in prey density, the number of prey consumed increased, then levelled off and the proportion of prey consumed decreased. When compared with control, no significant differences across treatments were observed in the attack rate and handling time of the predator stages. The adult female showed maximum searching efficiency with attack rate and handling time ranging between 0.226–0.204 h−1 and 3.069–3.457 h, respectively, across fungicide treatments. This study suggests that even under the exposure of fungicides, N. longispinosus could possess a promising predatory potential against T. urticae on tomato.

Can the native crab Thalamita danae be an effective biological control agent of the invasive mussel Xenostrobus securis in Hong Kong?

AbstractLocal predators are often considered effective and environmentally-friendly control agents to limit invasive species. Such biological control, however, depends on both the predator prey preferences and performances, which are in turn affected by variations in the physical environment. This study investigated the predation of the swimming crab Thalamita danae on the invasive mussel Xenostrobus securis under different salinity and thermal conditions. Xenostrobus securis, which is native to Australia, has spread to Hong Kong since the last decade, causing adverse ecological and economic impacts. Laboratory experiments evaluated the prey preferences and feeding behaviours of the crab on both the native mussel Brachidontes variabilis and the invasive X. securis under different typical salinities (15, 25, and 35‰) and temperatures (22 and 28 °C). The crab did not show clear preference toward either the invasive or the native mussels. Although the shell morphology of the invasive mussels lowered handling time as compared to the native mussels, the crab consumption rate was similar between the mussel species. The survival and predation rate of the crab were, however, substantially reduced under low salinities (&lt; 15‰) where X. securis could be found. Thalamita danae, therefore, is a potential predator of X. securis, but such predation is only possible under normal, oceanic conditions. In hyposaline, estuarine/ freshwater environments where X. securis can survive, however, T. danae performs poorly and, as a result, such physical conditions may represent a predator refuge for the mussels to invade local ecosystems.

Trophic role and predatory interactions between the blue crab, Callinectes sapidus, and native species in open waters of the Ebro Delta

The Ebro Delta has become a major blue crab (Callinectes sapidus) fishery area in the NW Mediterranean, but there is limited information on factors controlling the abundance of populations in open waters, a crucial habitat for ovigerous females. Here, we use a stable isotope approach (δ15N and δ13C), to assess blue crab trophic position, the potential consumption of food items using mixing models, and the isotopic niche overlap with local commercial species. For Octopus vulgaris, a potential blue crab key predator, a trophic enrichment experiment was also conducted to further assess predation control in wild populations. The blue crab showed 1.6 times higher trophic position than in other habitats of the Ebro Delta, and similar to that found in the harbor crab, Liocarcinus depurator, and several predatory fish. Additionally, the isotopic niche of blue crabs showed overlaps from 46.2 to 14.9% with native predators, and mixing models also suggest even dietary contributions throughout the food web. For O. vulgaris, field results showed a trophic position of 3.93, lower than that of blue crab, and lower δ15N signatures were also obtained in a captivity experiment drawing negative fractionation (−1.1‰). We conclude that high dietary contribution of animal prey might provide a high protein diet that could be crucial for allowing the maintenance of a large local population, but the overall functional trophic similarity could also disfavor local native species. The similarity between experimental fractionation and field differences between predator and prey (−1.6‰) suggests that predation of blue crab is possible, but further research is needed to clarify the metabolic routes involved in octopus δ15N fractionation.